JPH1075164A - Gate drive circuit for voltage control-type switching element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the gate driving circuit of a voltage control-type switching element in a simple constitution which can be turned off with a small loss and a low surge voltage. SOLUTION: The gate signal supplying circuit of an IGBT1 constituting a main circuit of a power converter is provided as a duplex constitution of two circuits. The gate signal supplying circuit is composed of a switching circuit for control 3-1 (3-2) for switching a gate voltage for turn-on and a gate voltage for turn-off, and a gate resistance 2-1 (2-2). At the time of turn-off, after an turn-off operation of one switching circuit for control 3-1, a turn-off operation of the other switching circuit for control 3-2 is executed after the lapse of a fixed time. Thus, a gate charge decreasing speed just after the start of a turn-off when the surge voltage is the maximum can be slowed, and the gate charge decreasing speed can be increased after a circulating diode has been turned on, and the main cause of the generation of a surge voltage is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gate drive circuit for a voltage-controlled switching element (such as an IGBT), and more particularly to a technique for reducing a surge voltage at turn-off.

[0002]

2. Description of the Related Art A voltage-controlled switching element such as I
In a power converter using a GBT, a surge voltage generated when the IGBT is turned off causes problems such as a decrease in operating voltage and an increase in switching loss. In order to reduce the surge voltage, the following measures are taken.

(A) To reduce the switching speed. IG
FIG. 6 shows a BT gate peripheral circuit, and FIG. 7 shows a corresponding gate drive circuit. In the figure, 1 is an IGBT,
2 is a gate resistor, 3 is a switching circuit for turn-on / turn-off control, and 4 is a power supply for turn-on (voltage + Vc).
c) Reference numeral 5 denotes a turn-off power supply (voltage -Vee).
The switching circuit 3 for turn-on / turn-off control includes:
For example, transistors TR1 and TR2 are connected in series, a gate resistor 2 is connected to the connection point, and a + Vcc connection driver DR1 and a -Vee connection driver DR2 are connected to the base.

When viewed from the driving driver side, the gate of the IGBT 1 is a capacitor (gate capacitance C shown in FIG. 6).
g). This is the resistance value Rg of the gate resistor 2.
A smaller value means that the charge of the capacitor can be quickly taken in and out. Therefore, the switching speed increases as the resistance value Rg decreases, and conversely, the switching speed decreases as the resistance value Rg increases. That is, the switching speed of the IGBT 1 can be adjusted by the gate resistor 2.

Since the surge voltage is a voltage generated when the IGBT 1 is rapidly turned off, the surge voltage can be suppressed low by increasing the gate resistance 2, that is, by reducing the switching speed.

(B) A snubber circuit for absorbing a surge voltage is added. The surge voltage is generated by the energy stored in the floating inductance (wiring inductance) of the IGBT main circuit. Therefore, if a snubber circuit is attached to the IGBT and energy is absorbed in the snubber circuit, the surge voltage can be suppressed low. 8 and 9 show typical snubber circuits.

The snubber circuit 21 shown in FIG. 8 has a configuration in which a resistor Rs and a capacitor Cs are connected in series, and the snubber circuit 22 shown in FIG.
Is a configuration in which a diode Ds is connected in parallel with the resistor Rs' to reduce the transient equivalent resistance.
Are connected in parallel.

[0008]

The above measures have the following problems.

Problem (A) When the switching speed is reduced, the surge voltage is reduced, but the time required for switching is increased. Since an increase in the switching time leads to an increase in the turn-off loss of the switching element (IGBT1), the problem shifts to the cooling of the element. However, the cooling of the element is important in characteristics, and the switching speed cannot be unnecessarily reduced. .

Problem (B) When the snubber circuit 21 (or 22) is additionally provided, the circuit configuration becomes complicated, which leads to an increase in the number of parts and man-hours.
Also, since the switching speed of recent IGBTs is quite high, the snubber circuit 21 (2) shown in FIG.
2) The wiring inductance Ld of the device itself cannot be ignored (there is no limit in shortening the wiring length of the snubber circuit), and the effect of the snubber circuit is limited. In particular, IG
In the case of BT, a sufficient effect cannot be expected.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances. By multiplexing gate signal supply circuits, a gate drive of a voltage control type switching element which can be turned off with a small circuit loss and a low surge voltage with a simple circuit configuration. It is intended to provide a circuit.

Further, the present invention provides a voltage control type which can be turned off with a small loss and low surge voltage with a relatively simple circuit configuration by adding a dedicated circuit for initial turn-off instead of duplicating the gate signal supply circuit. It is an object to provide a gate drive circuit for a switching element.

[0013]

According to the present invention, there are provided a plurality of gate signal supply circuits for selectively supplying a turn-on gate voltage and a turn-off gate voltage to a gate of a voltage-controlled switching element via a switching circuit and a gate resistor. At the time of turn-off, one operation is performed from an early stage of the turn-off, and the other operation is performed after a predetermined time.

According to the present invention, there is provided a gate drive circuit of a voltage-controlled switching element for selectively supplying a turn-on gate voltage and a turn-off gate voltage to a gate of the voltage-controlled switching element via a switching circuit and a gate resistor. Common terminal of switching circuit and Gnd
A turn-off initial dedicated circuit having a discharge path between levels is provided, and at the time of turn-off, first, only the turn-off initial dedicated circuit is operated, and after a predetermined time, the switching circuit is turned off and the turn-off initial dedicated circuit is turned off. It is characterized by the following.

[0015]

FIG. 1 shows an embodiment of the present invention. In the figure, reference numeral 1 denotes an IGBT, 2-1 and 2-2 denote gate resistors, 3-1 and 3-2 denote turn-on / turn-off control switching circuits, and two gate signal supply circuits of the IGBT 1 are provided.

Next, the operation will be described. When turning off the IGBT 1, first, only one gate signal supply circuit, for example, only the control switching circuit 3-1 is operated. That is, the control switching circuit 3-1 is switched to the negative power supply. In this state, the other gate signal supply circuit (on the side of the control switching circuit 3-2) remains turned on, and when the power supply voltage is ± Vg and the value of the gate resistance is Rg, the voltage state is as shown in FIG. ). When this is viewed from the IGBT 1, it becomes equivalent to the circuit shown in FIG. That is, R is applied to the gate of IGBT1.
0 (V) is applied through a resistor of g / 2.

For this reason, the initial charge reduction speed of the gate of the IGBT 1 is determined by one gate signal supply circuit (see FIG. 8).
This is equivalent to the case where the surge voltage is reduced by setting the value Rg of the gate resistance to be relatively large (half the voltage and half the resistance). Therefore, the same voltage occurs as the surge voltage. Then, after a certain period of time has passed (after the freewheel diode and the like are turned on and the cause of surge voltage generation is reduced), the other control switching circuit 3-2 also performs a turn-off driving operation. When turn-off driving is performed by both gate signal supply circuits, the charge reduction speed becomes faster, and the switching speed becomes higher than that in the case of FIG. As a result, the switching speed can be increased at the same surge voltage.

In the above-described embodiment, the gate signal supply circuit has two circuits (double), but the gate signal supply circuit can be multiplexed to three or more circuits. In this case, by appropriately selecting the number of circuits and the value of the gate resistance, it is possible to finely adjust the gate charge reduction speed at the time of turn-off, and it is possible to expect more effective (low switching loss, low surge voltage) switching operation.

FIG. 3 shows another embodiment of the present invention. In the figure, 1 is an IGBT, 2 is a gate resistor, 3 is turn-on.
Switching circuit for turn-off control, 4 is power supply for turn-on (voltage + Vcc), 5 is power supply for turn-off (voltage-
Vee). The turn-on / off control switching circuit 3 includes, for example, transistors TR1 and TR2 connected in series, a gate resistor 2 at the connection point thereof, a + Vcc connection driver DR1 at the base, and a -Vee connection driver D at the base.
R2 is connected to each other. Reference numeral 6 denotes a turn-off initial dedicated circuit, which comprises a Gnd connection driver DR3, and a transistor TR3 which is turned on / off by this output. The collector of the transistor TR3 is a gate resistor 2, and the emitter is a connection point between the turn-on power supply 4 and the turn-off power supply 5. (Gnd point).

The turn-off initial dedicated circuit 6 has a function of extracting electric charges when the potential of the driver output is higher than the Gnd level. Also, the Vcc connection driver DR1 and -Ve
The e-connection driver DR2 is configured to be able to be driven independently (in a normal driver, the operations are inverted with each other).

Next, the operation will be described. At the time of turn-on, the turn-off initial dedicated circuit 6 is not driven, but is driven in the same manner as the normal gate driver at the Vcc connection driver DR1. Therefore, the characteristics at the time of turn-on are the same as those of a normal driver.

At the time of turn-off, the + Vcc connection driver D
After turning off the R1 part, the turn-off initial dedicated circuit 6
Turn on. In this state, the gate of the IGBT 1 is connected to the Gnd level through the gate resistor 2 and the transistor TR3, as shown by the bold line in FIG. In a normal gate driver, the connection to the -Vee power supply is performed from the beginning, and the gate charge extraction force at this stage is weaker in the present embodiment, and the switching is performed slowly. Thereby, the surge voltage is reduced.

At a stage where the turn-off has progressed to some extent and the generation factor of the surge voltage has been reduced, the portion of the -Vee connection driver DR2 is turned on as shown by the thick line (also indicated by the arrow b) in FIG. At the same time, the turn-off initial dedicated circuit 6 is turned off. As a result, the switching speed thereafter becomes equal to that of a normal driver.

Therefore, when the gate resistor 2 has the same value, in this embodiment, even if the surge voltage can be reduced, the switching speed becomes slow due to the operation period of the turn-off initial dedicated circuit 6, but the surge voltage occurs most. Since the switching speed immediately after switching can be reduced, the gate resistance 2 can be set to a smaller value. When Vcc = Vee, the gate resistance 2 can be reduced to approximately half the value. In this case, an increase in the switching time due to the operation of the turn-off initial dedicated circuit 6 increases in the subsequent operation period of the -Vee connection driver DR2. Is sufficiently compensated for by the reduction of

[0025]

As described above, according to the present invention, the gate charge decreasing speed immediately after the start of turn-off, at which the surge voltage becomes the highest, is slowed down, and after the freewheeling diode is turned on to reduce the surge voltage generation factor, the gate voltage is reduced. Low switching loss and low gate loss
Switching operation at a low surge voltage becomes possible. Further, even if the driver configuration is slightly complicated, the snubber circuit can be greatly reduced and the snubberless can be achieved by adopting an appropriate driver configuration, which is very advantageous as a whole device.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing an embodiment of the present invention.

FIG. 2 is an operation explanatory diagram when only one gate signal supply circuit in one embodiment is turned off, and FIG.
FIG. 4 is a circuit diagram showing a circuit voltage state, and FIG. 4B is an equivalent circuit diagram viewed from the IGBT side.

FIG. 3 is a circuit diagram showing another embodiment of the present invention.

FIG. 4 is a circuit diagram for explaining an operation state when a turn-off initial dedicated circuit according to another embodiment is operated.

FIG. 5 is a circuit diagram illustrating an operation state when a −Vee connection driver according to another embodiment is operated.

FIG. 6 is a circuit configuration diagram showing a conventional general gate peripheral circuit.

FIG. 7 is a circuit diagram showing a gate drive circuit corresponding to the gate peripheral circuit of FIG. 6;

FIG. 8 is a circuit diagram illustrating an example of a typical snubber circuit.

FIG. 9 is a circuit diagram showing another example of a typical snubber circuit.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... IGBT 2, 2-1 and 2-2 ... Gate resistance 3, 3-1 and 3-2 ... Switching circuit for turn-on / turn-off control 4 .... Power supply for turn-on 5 .... Power supply for turn-off 6 .... Dedicated circuit for initial turn-off TR1 TR3: Transistors DR1 to DR3: Driver

Continued on the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical display location // H02H 9/04 H03K 17/56 Z

Claims (2)

[Claims] 1. A plurality of gate signal supply circuits for selectively supplying a turn-on gate voltage and a turn-off gate voltage to a gate of a voltage-controlled switching element via a switching circuit and a gate resistor are provided. A gate drive circuit for a voltage-controlled switching element, wherein the operation is performed from an early stage of turn-off and the other operation is performed after a predetermined time. 2. A gate drive circuit for a voltage-controlled switching element, wherein a gate voltage for a turn-on and a gate voltage for a turn-off are selectively supplied to a gate of the voltage-controlled switching element via a switching circuit and a gate resistor. A turn-off initial dedicated circuit having a discharge path between the common terminal and the Gnd level is provided. At the time of turn-off, only the turn-off initial dedicated circuit is operated first, and after a predetermined time, the switching circuit is turned off and the turn-off initial dedicated circuit is turned off. A gate drive circuit for a voltage-controlled switching element, wherein the gate drive circuit comprises: